Immunotherapy, in medicine, refers to an array of treatment strategies based on the concept of modulating the immune system to achieve a prophylactic and/or therapeutic goal.
In the past few years, immunotherapy has been used for the treatment or the prevention of several pathologies, particularly cancers. Since the development of the cell fusion technique for the production of monoclonal antibodies, a vast number of monoclonal antibodies have been produced by researchers. Thenafter, other techniques have been developed for the generation of monoclonal antibodies, including the B cell hybridoma technique and the EBV hybridoma technique to produce human monoclonal antibodies.
Monoclonal antibodies (Mab) can be developed to target almost any epitope. The property of specific recognition and binding to particular cells/molecules has encouraged the development of Mabs as diagnostic and therapeutic reagents for a variety of disease states. Recombinant DNA techniques have been used to produce chimeric or humanized antibodies to adapt their administration to humans. Currently, several monoclonal antibodies are commercialized and available for the treatment of cancers, infectious diseases, immune diseases etc. such as RITUXAN®, HERCEPTIN®, AVASTIN®, . . . .
Monoclonal antibodies are targeted molecules and able to localize within a specific zone (cells, tissues . . . ) such as a tumor tissues. This property has also led to the development of Mabs conjugated to various substances (payloads) in an effort to target specific molecules in the tumor sites called tumoral antigens. Such substances (payloads) can be toxins, drugs, radionuclides, prodrug compounds . . . . Many of these linkages involve the chemical conjugation of the reactive moiety (payload) with a given preparation of antibody, a process which can be cumbersome and subject to variation (U.S. Pat. No. 4,671,958).
Among these new molecules, the immunocytokines are of particular interest. Said immunocytokines correspond to fusion proteins comprising an antibody and a cytokine. These proteins retain both antigen-binding capacity and cytokine activity.
The cytokines are a category of signalling proteins and glycoproteins that, like hormones and neurotransmitters, are used extensively in cellular communication. While hormones are secreted by specific organs into the blood, and neurotransmitters are related to neural activity, cytokines are a more diverse class of compounds in terms of origin and purpose. They are produced by a wide variety of hematopoietic and non-hematopoietic cell types and can have effects on both nearby cells or throughout the organism, sometimes strongly depending on the presence of other chemicals. The cytokine family consists mainly of smaller, water-soluble proteins and glycoproteins with a mass of between 8 and 30 kDa. Cytokines are critical to the functioning of both innate and adaptive immune responses. They are often secreted by immune cells which have encountered a pathogen as a way to activate and recruit more immune cells and increase the system's response to the pathogen. However, apart from their role in the development and functioning of the immune system, cytokines are also involved in several developmental processes during embryogenesis.
Among the cytokines, interleukin 15 (IL-15) is a cytokine with structural similarity to IL-2 that is secreted by mononuclear phagocytes (and some other cells) following infection by virus(es) or indirect stimulation by cells recognized as non-self or debilitated. This cytokine induces cell proliferation of natural killer cells; cells of the innate immune system whose main role is to kill virally infected cells. The protein encoded by this gene is a cytokine that regulates T and natural killer cell activation and proliferation.
The construction of immunocytokines on the basis of IL-15 would thus be of particular interest for the combination of the tumor-targeting assets of tumor-specific antibodies with the immunomodulatory effects of interleukin 15. Several immunocytokines using notably interleukin-2 (IL-2) have been already obtained and demonstrated very interesting and encouraging results in phase 2 oncology clinical trials. Some examples of these fusion proteins are described in several patent applications (U.S. Pat. No. 5,645,835, EP 0,305,967, WO 86/01533, EP 0,439,095, and WO 85/00974).
Thus, interleukin 15-based immunocytokine has been produced in HEK-293 cells and is disclosed in International patent application PCT WO 2007/128563 and in KASPAR et al. (Cancer Research, vol. 67(10), p: 4940-4948, 2007).
Nevertheless, the inventors established that such interleukin 15-based immunocytokines have a very limited interleukin 15 activity, and that their production is very difficult notably in CHO cells with low yield and many protein contaminants.
Thus, there is still a need for interleukin 15-based immunocytokines that can be used in immunotherapies.